The invention relates to a method for measuring and keeping constant the water content in a highly heated salt bath, where the pressure of the water vapor over the salt bath depends on or corresponds to the quantity of water in the bath, and also to a device for performance of the method.
As is generally known, the quenching or cooling of heat-treated materials during the process of hardening and tempering is often done in a salt bath whose action is greatly influenced, for example, by the chemical composition of the bath, the temperature of the bath, the movement of the salt in the bath itself, the degree of fouling of the bath and also its water content. It has been found in practice that problems are posed in particular by regulation of the water content or proportion in the salt bath.
The present invention relates to an improvement of the quenching or cooling effect, and hence in the hardening and tempering of the materials. This improvement comprises a method and device wherein the water content is continuously measured and kept constant, or at any rate the required percentage or proportion is maintained in the salt bath, with due allowance made for the relatively high temperature. In this connection it can be taken as generally known, that the temperature in such a salt bath may be between 150.degree.-550.degree. C, and moreover that a relatively small loss of water can, for instance, substantially affect the hardness of the metal being hardened and tempered. Tests have shown, in fact, that in the case of bolts made of plain carbon tool steel which are heat-treated at temperatures of 850.degree.-930.degree. C, followed by cooling in a salt bath at a temperature between 180.degree.-200.degree. C, a 0.2 vol % loss of water from the salt bath serves to lower the hardness from 62 HRc to 45 HRc. This shows how very important it is to keep the water content or proportion of water constant in salt baths of this kind.